Transform article HTML string: ensures language-switcher and article-top-nav
with a back-to-news link are present. Idempotent — safe to call multiple times.
Parameters
content: string
Original HTML string
baseSlug: string
Article base slug without directory prefix (e.g. "2026-01-01-article")
Transform article HTML string: ensures language-switcher and article-top-nav with a back-to-news link are present. Idempotent — safe to call multiple times.